smalloc: don't mix malloc() and new char[]

It's technically undefined behavior to mix malloc with delete[] and
new char[] with free().  smalloc was using new char[] in one place and
malloc() in another but in both cases the memory was freed with free().

PR-URL: https://github.com/iojs/io.js/pull/1205


Reviewed-By: Trevor Norris <trev.norris@gmail.com>